Some semiconductor devices for driving a load with electric power which is supplied from a power supply by switching of a power semiconductor switching element have a protection function in order to prevent overcurrent from flowing through the power semiconductor switching element, resulting in a breakdown of the element (see JP-A-2014-138521 and WO 2016/143382 for instance).
Such a type of semiconductor device determines whether overcurrent is flowing in a power semiconductor switching element based on whether the value of the output voltage of the power semiconductor switching element is higher or lower than a predetermined threshold. However, when the power semiconductor switching element is turned on, at first, the output voltage of the power semiconductor switching element is lower than the predetermined threshold for determining that the power semiconductor switching element is in a normal ON state. Therefore, if determination is performed in that state, it may be erroneously determined that the power semiconductor switching element is not in the normal ON state. In other words, an overcurrent state may be erroneously detected. For this reason, a filter for setting a delay time may be provided such that after the power semiconductor switching element is turned on, when the delay time elapses, in other words, when the output voltage reaches the predetermined threshold for determining that the power semiconductor switching element is in the normal ON state, the filter outputs the result of comparison between the value of the output voltage and the threshold to the control circuit side to perform determination.
In the meantime, during a normal operation, the voltage of the power supply may drop for any reason. In this case, even if the delay time set by the filter elapses, the output voltage of the power semiconductor switching element may not reach the predetermined voltage value for determining that the power semiconductor switching element is in the normal ON state. Therefore, an overcurrent state may be erroneously detected, and the whole of the semiconductor device may not be able to normally operate.